The present invention relates generally to a hermetically sealed plastic container and more particularly to a hermetically sealed plastic container in which a container closure member is friction welded to a container body.
Various methods have been employed for many years to produce easy open, pull-top closures for cans. In the past, these closures have been manufactured from aluminum and, more recently, from steel sheet stock. These closures include a pull tab and a near fracture score in the container closure to initiate removal of the tab. The contents of the package are protected from oxygen by the impervious metals utilized in the container. The closure is attached to a metal and/or plastic can body by conventional double-seaming technology.
Although these container closures are in widespread use, they are not without disadvantages. Removal of the metallic closure panel typically exposes rough, razor-sharp edges, which may inflict serious injury on consumers. These metallic containers are also not suitable for microwave cooking applications.
Plastic containers have become increasingly popular for use in microwave cooking. When consumer products are sold in plastic containers, the consumer may use the same container in which the product was sold to heat the product in a microwave oven. However, if a metallic lid or closure is used to seal the plastic can body, a metallic rim remains on the container body when the closure is removed to open the container. The metallic rim may cause field disruptions in the microwave oven, which in turn may cause serious electrical discharges within the microwave oven.
The metallic closure may also have aesthetic and marketing disadvantages, and metallic container ends may not be perceived as an upscale packaging medium.
Plastic hermetically sealed containers may also be suitable for use in applications such as aseptic, hotfill and retort applications. Such uses require a high-strength seal between the closure and the container body in addition a reliable hermetic seal.
Since it is desirable to provide a container closure which may be easily opened or removed, plastic container closures typically include a layer of tearable plastic material. Tearable plastic materials, however, are typically gas-permeable. Therefore, closures requiring a hermetic seal typically include a layer of gas-impermeable material bonded to the layer of tearable plastic. For example, U.S. Pat. No. 4,212,409 (Jeppsson) discloses a laminated easy open closure for a container. The closure includes a top plastic layer and a metallic foil layer bonded together, with a tear-line formed in the plastic layer. The tear line is provided to facilitate opening of the container to which the closure is affixed. The closure is sealed to the container body by means of a sealing laminate disposed on the bottom surface of the closure and around the outer peripheral edge of the container body.
U.S. Pat. No. 4,513,876 (Buckner) and U.S. Pat. No. 4,533,063 (Buckner et al.) disclose arrangements which provide an easy open closure made of a plastic/foil laminate in which a plastic layer is bonded to the top surface of the foil and is weakened to form a tearline. In these arrangements a second inner layer made of a plastic material such as polyethylene or polypropylene is bonded to the inner surface of the foil. The inner plastic layer is used to heat seal or weld the container closure to a container body.
U.S. Pat. No. 4,693,390 (Hekal) discloses an easy open closure which includes an aluminum foil layer and a plastic base layer. The base layer is positioned inside the closure and is provided with a score line, which facilitates the opening of the closure. The plastic container is integrally heat bonded to the plastic base layer of the closure.
These containers have the disadvantage that they are relatively expensive to manufacture. First, these arrangements typically contain two layers of plastic, one bonded to each surface of the barrier material. The bottom layer of plastic is provided to seal the closure to the container body. This additional plastic layer increases the cost of materials for the container. Second, if an injection molding process is used to manufacture the plastic container components, the additional second plastic layer complicates the manufacturing process. Typically, one of the plastic layers is first injection molded onto the layer of barrier material. The second plastic layer is subsequently added in a separate process step. Thus, the manufacture of this three layered closure is relatively time consuming.
As discussed above, several applications require plastic containers which have a high-strength, reliable seal between the container body and the container closure. The process of friction or spin-welding has been heretofore used to provide a high-strength seal between a plastic container and a plastic closure. For example, U.S. Pat. No. 3,800,400 (Mistarz) U.S. Pat. No. 3,499,068, (Brown); and U.S. Pat. No. 3,297,504, (Brown, et al.) teach spin-welding methods and apparatus for assembling and joining thermoplastic container sections, which patents are incorporated herein by reference.
It is therefore an object of the present invention to provide a plastic hermetically sealed container which has a high-strength seal between the container body and the closure.
It is another object of the present invention to provide a container which may be easily and economically manufactured.
It is still a further object of the present invention to provide a hermetically sealed plastic container which may be easily opened.